Conventionally, an image forming apparatus is known in which a light beam emitted by a light source is reflected by a reflector and is emitted to a photosensitive member. This image forming apparatus has a forced signal output circuit, a light receiver, and an image data output circuit. The forced signal output circuit outputs a forced lighting signal. The light beam emitted from the light source based on the forced lighting signal and reflected by the reflector is received by a light receiver. The image data output circuit outputs an image data signal at timing corresponding to reception of the light beam by the light receiver. The light beam emitted from the light source based on the image data signal and reflected by the reflector forms a scanning line on the photosensitive member.
In such image forming apparatus, a forced lighting signal outputted from the forced signal output circuit and an image data signal outputted from the image data output section are inputted to an OR circuit, and a lighting signal that is a logical sum of the forced lighting signal and the image data signal is outputted to the light source.